Extraction with sulphur dioxide



y 1944- r R. E. TAN NlCH 2,349,473

EXTRACTION WITH SULPHUR DIOXIDE Filed Sept. 14, 1942 Inhibitor LightHydroform ed Distillate ,Gondenser Hydrafarming Equipment Distillate llKS0 Plant Charge Tank 6/? V .l4 Heavy Hydrotarmed Distillate A 7' TOR/V5Y Patented May 23, 1944 EXTRACTION WITH SULPHUR DIOXIDE Richard E.Tannich, Baytown, Tex., assignor to Standard Oil Development Company, acorporation of Delaware Application September 14, 1942, Serial No.458,311

4 Claims.

The present invention is directed to the S02 extraction of petroleumfractions containing olefins.

The extraction of petroleum fractions with S: is a well known procedurein refinery operations. For the most part, it has been practiced on acommercial basis on virgin distillates. Attempts to apply it to crackeddistillates have led to operating difliculties, such as coking of heatexchangers and of other equipment which is heated in the course of theoperation to separate S02 from the extract and the rafi'inate. Thistrouble has been particularly pronounced in operations in whichhydroformed naphthas have been employed as the feed stock for theextraction.

It has now been found that the aforesaid difficulty can be avoided if anoxidation inhibitor is incorporated in the hydrocarbon fraction beforeit is contacted with the sulphur dioxide and maintained in the mixturewhile the S02 is in contact with the hydrocarbons. It is preferable toadd the inhibitor to the hydrocarbon fraction immediately after thetreatment which results in the formation of olefins and before thefraction has an opportunity to come into contact with air. In theordinary operation, it is advantageous to subject the fractionimmediately after the conversion treatment which produced the olefins toa distillation to remove the light ends, thereby automaticallyeliminating any oxygen that may have been picked up by the fraction.Then the inhibitor is added to the remainder.

The inhibitor to be employed may be any one of the commonly knownoxidation inhibitors which are soluble in petroleum. A suitableinhibitor is isobutyl-p-amino phenol. This inhibitor may be employed inamounts varying from about 0.05 to 0.50 lbs. per 1,000 gals. ofpetroleum. Greater amounts may be employed, but are not required.Amounts that render the cost undesirably high are not attractive for theadditional reason that they are inefiective. other inhibitors of thephenolic or amino type may be employed. A particularly suitable class ofinhibitors are those which are known in the art as gum inhibitors inmotor fuels. A preferred type of inhibitor is a cut of petroleum phenolsobtained by extracting heavy cracked distillates boiling in the range ofabout 250-700 F. with 30-50 Baum sodium hydroxide solution andacidifying the extract to release the phenols. These petroleum phenolsare efiective in quantitles as low as 0.25 lb./1,000 gals. of petroleumfraction.

One procedure which may be followed in the practice of the presentinvention is illustrated in the accompanying drawing, in which thesingle figure is a front elevation, in diagrammatic form, of a plantsuitable for such procedure.

Referring to the drawing in detail, numeral l designates a feed line forintroducing a petroleum fraction, such as virgin naphtha, intoconversion unit 2 in which is effected an operation such as cracking,hydroforming, cyclization, or the like, in which hydrogen is split ofifrom hydrocarbons. The efiluent from this unit is conducted, by line 3,into a distillation unit 4 in which light ends, including any oxygenwhich may be contained in the distillate, are taken off overhead throughline 5. The residue is drawn oii from the bottom through line 6 anddischarged into a second distillation unit I, from the top of which iswithdrawn 9. fraction of the desired boiling range for extraction withS02 through line 8. Connected to line 8 is a branch line 9 forintroducing regulated amounts of a selected inhibitor from a storagetank l0 into the hydrocarbon stock, which is then fed into a storagetank II.

The feed stock from the storage tank is conducted, byline I 2, into anS0: extraction unit l3, in which is a feed line H! for $02, an exit lineI5 for S02 extract, and an exit line [6 for S02 raflinate. The extractis then conducted into a system for the separation of the SO: from theextract, which includes heat exchangers and other equipment which ismaintained at an elevated temperature. It is in this heated recoveryequipment that dimculty was previously encountered in the form of cokedeposition. This coke deposition has been considerably minimized, infact, almost to the point of complete prevention, by the use of theinhibitor in the manner described above.

The nature and objects of the present invention having been thusdescribed and illustrated, what is claimed as new and useful and isdesired to be secured by Letters Patent is:

1. In a method in which a petroleum fraction containing olefins isextracted with S02, the steps of introducing into said petroleumfraction prior to its contact with S0: an oxidation inhibitor andmaintaining said inhibitor in the mixture until the S02 is separatedfrom the hydrocarbons.

2. In a method in which a petroleum naphtha is subjected to a thermalconversion during which olefins are formed, and then to extraction withsulphur dioxide, the steps of introducing into gether with any oxygenwhich may be present, are removed, and then adding an oxidationinhibitor to the residuaI naphtha prior to the extraction thereof withS02 whereby said inhibitor is present at all times while said naphtha isin contact with $02.

4. A method according to claim 1 in which the inhibitoremployed is apetroleum phenol.

' RICHARD EZTANNICH.

